Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $56.64   4.242%   $59.0427   $59.04   $59.05   $59.00  
  Purchase #2 $166.81   6.160%   $177.0855   $177.09   $177.10   $177.10  
  Purchase #3 $129.30   5.115%   $135.9137   $135.91   $135.90   $135.90  
  Purchase #4 $109.90   9.120%   $119.9229   $119.92   $119.90   $119.90  
  Purchase #5 $32.32   12.364%   $36.316   $36.32   $36.30   $36.30  
  Purchase #6 $12.84   11.205%   $14.2787   $14.28   $14.30   $14.30  
  Purchase #7 $205.33   8.432%   $222.6434   $222.64   $222.65   $222.60  
  7 purchase totals = $713.14       $765.2029   $765.20   $765.20   $765.10